1. Field of the Invention
The present invention relates to a liquid crystal display device having an electrostatic discharge protection circuit, and a method of manufacturing the same.
2. Discussion of the Related Art
A liquid crystal display (LCD) device is a flat panel display device in which an electric field is applied to liquid crystal molecules having fluidity of liquid and optical characteristics of a crystal to change an optical anisotropy of the liquid crystal molecules. The liquid crystal display device has low power-consumption and a small volume as compared with the conventional cathode ray tube. In addition, the liquid crystal display device can be manufactured in a large size and can display high-definition images. As a result of these advantages, the liquid crystal display device is extensively used.
A typical liquid crystal display device includes a liquid crystal display panel for displaying images and a driving circuit for applying a driving signal to the liquid crystal display panel. The liquid crystal display panel includes a first substrate and a second substrate that are combined with each other while being spaced apart from each other and a liquid crystal layer interposed between the first substrate and the second substrate.
Liquid crystal display devices can have various types of modes depending on characteristics and a pattern structure of the liquid crystal molecules. The liquid crystal display device includes a Twisted Nematic (TN) Mode liquid crystal display device, a Multi-Domain Mode liquid crystal display device, an Optically Compensated Birefringence (OCB) Mode liquid crystal display device, an In-Plane Switching (IPS) Mode liquid crystal display device, and a Vertical Alignment (VA) Mode liquid crystal display device.
In the TN Mode liquid crystal display device, directors of the liquid crystal molecules are aligned such that the directors are twisted in 90 degrees. A voltage is applied to the liquid crystal molecules to control the directors of the liquid crystal molecules.
In the Multi-Domain Mode liquid crystal display device, a pixel is divided into a plurality of domains such that the domains have main viewing angles different from each other, thereby realizing a wide viewing angle.
In the OCB Mode liquid crystal display device, a compensation film is attached to an outer surface of the substrate to compensate for phase variation of light depending on a traveling direction of light.
In the In-Plane Switching Mode liquid crystal display device, two electrodes are formed on a single substrate such that the director of the liquid crystal molecule is twisted on a plane which is parallel to an alignment layer on the substrate.
In the VA mode liquid crystal display device, a major axis of the liquid crystal molecule is aligned perpendicularly to a vertical alignment layer by using a negative type liquid crystal molecule and the vertical alignment layer.
Meanwhile, a plurality of pixel regions arranged in a matrix are defined in the liquid crystal display device by crossings of gate lines for applying the driving signal with data lines for applying a graphic data signal. A pixel electrode and a thin film transistor (hereinafter, referred to as a “TFT”) that transfers a data signal applied from the data line, are disposed on each pixel region.
An electrostatic discharge protection circuit is formed in the liquid crystal display devices regardless of the mode of the liquid crystal display device in order to prevent elements and signal lines, such as gate lines, data lines and common voltage lines, from being damaged by static electricity generated from the outside or inside of the LCD device during the manufacturing process or when using the liquid crystal display device. The electrostatic discharge protection circuit is disposed between ends of the common voltage line, to which a common voltage is applied, the gate line and the data line.
However, when the liquid crystal display device is manufactured to have a small size with a high-resolution, the available space for forming the electrostatic discharge protection circuit is reduced, causing a difficulty in designing the electrostatic discharge protection circuit. In particular, since the electrostatic discharge protection circuit is formed by connecting a plurality of transistors to each other, if intervals between the gate lines or the data lines are narrow, a shorting-defect may occur between the lines during the manufacturing process.
Recently, various portable display devices have been extensively used for displaying a moving picture. These portable display devices are manufactured in a small size and require a high-resolution. Accordingly, an electrostatic discharge protection circuit suitable for a narrow space is highly desired.